Binocular correspondence is the study of how the two monocular images are correctly fused in normal binocular vision, creating a sense of depth and permitting the detection of small disparity differences as in fine stereoacuity. Psychophysical experiments on a repetitive stimulus, the ambiguous stereogram of the "wallpaper effect", will be used to probe the operations of normal fusion. The basic stimulus for the proposed research is a small grid of bright points displayed haploscopically. Manipulation of the disparity of the edges of this display can force the fusion of this target in several different depth planes, without the intervention of changes in convergence. Two theoretical models of fusion will serve as a framework for the proposed experiments. Specifically, the proposed research will examine three questions: 1) If the edge effects are propagated via cooperative interactions between local disparity detecting neural elements, what are the spatial and temporal arrangements which produce the change in the apparent depth of this target? 2) If the edge effects represent disparity responses of low spatial frequency channels, how do the low spatial frequency channels surpress the disparity signals of higher spatial frequency channels? 3) If fusional processes depend on interactions between competing disparities, how is the stereoacuity for a target lying one plane affected by adjacent targets lying in other depth planes? This research will supply fundamental information about normal binocular fusion. A preliminary study on patients with abnormal fusion, also part of the proposed research plan, will examine how abnormal binocular mechanisms respond to these grid stimuli.